Method of fabricating turning mirror using sacrificial spacer layer and device made therefrom

ABSTRACT

The present invention is a method of fabricating a waveguide using a sacrificial spacer layer. The first step in this process is to fabricate the underlying optical semiconductor structure. A trench is then etched in this structure resulting in an underlying L-shaped structure. A sacrificial spacer layer is deposited in the trench. The waveguide is created in the trench on the sacrificial spacer layer using a mask layer to angle the vertex of the L-shaped structure. User-defined portions of the sacrificial spacer layer are subsequently removed to create air gaps between the waveguide and the sidewalls of the trench in the optical semiconductor.

CROSS-REFERENCE TO RELATED APPLICATION

The present invention is a division of U.S. patent application Ser. No.11/472,225, entitled “METHOD OF FABRICATING TURNING MIRROR USINGSACRIFICIAL SPACER LAYER AND DEVICE MADE THEREFROM,” filed Jun. 16, 2006now U.S. Pat. No. 7,611,914.

FIELD OF THE INVENTION

The present invention relates to a semiconductor manufacturing processand, more specifically to a semiconductor manufacturing process formaking a device including integrally formed optical waveguides.

BACKGROUND OF THE PRESENT INVENTION

Integration of semiconductor lasers to planar optical components, suchas waveguides, semiconductor optical amplifiers (SOAs) and detectors, isimportant for photonic integrated circuit (PIC) applications. Whenworking with PICs it is essential to control reflections from theinterfaces between integrated photonic components. With proper design,interface reflections may be used to enhance performance of integratedlasers.

One method is to precisely space gaps between components to coherentlyenhance or reduce reflections from the interfaces. Prior art methodsdescribe the use of resonant and anti-resonant etched gaps used tocouple between lasers, SOAs and other lasers, taking advantage of theindex discontinuity across air gaps to selectively enhance or reducereflections across interfaces. A similar process has been demonstratedto create semiconductor lasers that make use of etched gaps in thesemiconductor material to enhance reflectivity of the laser mirrors. Atnear-infrared wavelengths, electron beam lithography is frequentlyrequired to provide the necessary resolution to define the etch masksused to create the resonant gaps.

“A Sub-Micron Capacitive Gap Process for Multiple-Metal-ElectrodeLateral Micromechanical Resonators,” Wan That Hsu, et al, TechnicalDigest, 14^(th) International IEEE Micro Electro Mechanical Conference,January 2001, discloses a process for fabricating a semiconductor havinggaps between metal electrodes and a polysilicon resonator resident onthe semiconductor. With this method, a sacrificial spacer layer isdeposited on a substrate. A polysilicon mechanical resonator is thendeposited and etched over the sacrificial layer, during which timeportions of the sacrificial layer are removed, and the metal electrodesare formed through electroplating on either side of the resonator. Thesacrificial layer is ultimately removed in its entirety. The presentinvention does not operate in the same manner as this process. The Hsuarticle is hereby incorporated by reference into the present invention.

“12 μm long edge-emitting quantum-dot laser,” S. Rennon, et al,Electronics Letters, May 2001, discloses a series of mirrors and acentral waveguide. Each of the mirrors and the central waveguide areetched. First order Bragg mirrors are patterned by electron-beamlithography on the rear side of the waveguide with air gaps etchedbetween the Bragg gratings. Third order mirrors are etched on the frontside of the waveguide. The first order air gaps between Bragg mirrorsdecrease diffraction loss in the laser (compared to third order airgaps) produced by this method. The present invention is not fabricatedin the same manner as the invention of Rennon, et al. Rennon, et al ishereby incorporated by reference into the specification of the presentinvention.

“Air Trench Bends and Splitters for Dense Optical Integration in LowIndex Contrast,” Shoji Akiyama, et al, Journal of Lightwave Technology,July 2005, discloses air trench waveguides, and specifically air trenchbend structures. It specifically describes a process for creating awaveguide with air trenches by first patterning the waveguide through adry etching process and thereafter patterning the air trenches through aphotolithography and dry etching process. The process of the presentinvention does not operate in this manner. Akiyama, et al is herebyincorporated by reference into the specification of the presentinvention.

U.S. patent application Ser. No. 09/412,682, entitled “SACRIFICAL SPACERFOR INTEGRATED CIRCUIT TRANSISTORS,” discloses a semiconductorintegrated circuit with a sacrificial sidewall. Specifically, temporarysidewalls are formed along the side of a gate electrode of asemiconductor. Source/drain regions are then formed on the semiconductoralongside the gate electrode, and the temporary sidewalls are removed,resulting in a space between the gate electrode and the source/drainregions. The present invention does not operate in this manner. U.S.patent application Ser. No. 09/412,682 is hereby incorporated byreference into the specification of the present invention.

U.S. Pat. No. 6,486,025, entitled “METHODS FOR FORMING MEMORY CELLSTRUCTURES,” discloses two methods for forming memory cell structures ina semiconductor integrated circuit. One method includes the use of asacrificial spacer layer formed adjacent to the sidewall of a capacitorof a field effect transistor formed on the semiconductor device. Adielectric layer is then formed alongside the spacer layer, throughwhich a bitline stud layer is formed that is electrically connected tothe source/drain regions of the field effect transistor. The sacrificialspacer layer is finally removed from the structure. The presentinvention operates in a different manner from this process. U.S. Pat.No. 6,486,025 is hereby incorporated by reference into the specificationof the present invention.

The methods described above effectively create air gaps in semiconductorstructures, however the processes are extremely inefficient as appliedto optical devices. Typically several masking and etching steps arerequired to create both the components, such as waveguides, and the airgaps in optical devices. This can be both time-consuming and costly.What is desirable in the art is to create an efficient, inexpensivemethod of creating optical semiconductor devices with integrated airgaps.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a method offabricating a waveguide turning mirror using a sacrificial spacer layer.

It is a further object of the present invention to provide a method offabricating a waveguide turning mirror using a sacrificial spacer layer,wherein a single sacrificial spacer layer operates to create an air gapand to adhere the waveguide to the semiconductor device.

It is another object of the present invention to provide a method offabricating a waveguide turning mirror using a sacrificial spacer layer,wherein a single sacrificial spacer layer operates to create an air gapand to adhere the waveguide to the semiconductor device and wherein awet etch is used to remove the sacrificial spacer layer.

The present invention is a method of fabricating a waveguide turningmirror using a sacrificial spacer layer. The first step of the method isselecting a base structure.

The second step of the method is depositing an undercladding layer onthe base structure.

The third step of the method is depositing a first cladding layer on theundercladding layer.

The fourth step of the method is depositing a core layer on the firstcladding layer.

The fifth step of the method is depositing a second cladding layer onthe core layer.

The sixth step of the method is depositing a cap layer on the secondcladding layer.

The seventh step of the method is depositing an upper contact on the caplayer. At this point the base optical semiconductor structure iscompleted.

The eighth step of the method is etching a trench in the resultantstructure, wherein the trench penetrates the upper contact, cap layer,second cladding layer, core layer, first cladding layer, and auser-definable portion of the undercladding and the trench is of auser-definable width, and wherein the resultant structure is etched suchthat it is substantially L-shaped and includes angling the vertex of thetrench.

The ninth step of the method is depositing a sacrificial spacer layeralong the trench.

The tenth step of the method is fabricating a waveguide on thesacrificial spacer layer.

The eleventh step of the method is removing the sacrificial spacer layerfrom the upper contact and a user-definable portion of the trench toproduce a waveguide turning mirror.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow chart of the steps of the present invention; and

FIG. 2 is a top plan view of a device manufactured in accordance withthe present invention.

FIG. 3 is a flow chart of the steps of an alternative embodiment of thepresent invention.

FIG. 4 is a top plan view of a device manufactured in accordance withthe alternative embodiment of the present invention

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention is a method of fabricating a waveguide turningmirror using a sacrificial spacer layer. FIG. 1 shows the steps of anexemplary embodiment of the method of the present invention. The presentinvention can operate using any coherent photonic emitter structure,however it will be described with respect to a specific epitaxialstructure. It will be understood by those of skill in the art that themethod may operate with any suitable coherent photonic emitterstructure, such as a standard bipolar, p-i-n semiconductor laser.

The first step 10 of the method of FIG. 1 is selecting a base structure.The base structure, for example a substrate, is composed of a compoundsemiconductor material and forms the base of the optical devicefabricated according to the method of the present invention. In thepreferred embodiment, the base structure is an n-type substrate, howeverthe base structure may also be a p-type or undoped substrate accordingto user preferences. Many such base structures are commerciallyavailable, or can be readily produced. The base structure may be of anysize, but preferably is approximately 3 inches in diameter.

The second step 12 of the method is depositing an undercladding layer onthe base structure. This undercladding improves the electricalefficiency of the semiconductor laser structure. The undercladding layercan be deposited by any conventional method, such as epitaxial growth,chemical vapor deposition, or high-pressure thermal oxidation. Theunder-cladding layer is composed of a conventional compoundsemiconductor material. In the preferred embodiment the under-claddinglayer is composed of a III-V semiconductor material, such as GaAs.

The third step 14 of the method is depositing a first cladding layer onthe undercladding layer. As is well known to those in the art, acladding layer is used in optical semiconductors to increase opticalconfinement in the active regions of the optical device. The firstcladding layer is a compound semiconductor material, many of which arecommercially available or easily producible. In the preferred embodimentthe first cladding layer is composed of AlGaAs. The first cladding layermay be deposited through any conventional means, such as epitaxialgrowth, chemical vapor deposition, or physical vapor deposition.

The fourth step 16 of the method is depositing at least one core layeron the first cladding layer. The core layer operates as the active layerfor the semiconductor laser. This core layer is composed of anappropriate compound semiconductor material that will be determinedbased on the material of the first cladding layer and the requiredoptical properties of the completed optical device. If more than onecore layer is required, a barrier layer with an electrical bandgap thatis larger than the bandgap of the core layers is used to separate thecore layers. In the preferred embodiment two core layers composed ofInGaAs are separated by a barrier layer composed of AlGaAs. The corelayer may be deposited on the first cladding layer by any conventionalmeans, such as epitaxial growth, chemical vapor deposition, or physicalvapor deposition.

The fifth step 18 of the method is depositing a second cladding layer onthe core layer. As was explained with reference to the third step 14 ofthe method, a cladding layer increases optical confinement in the activeregions of the optical device. The second cladding layer is preferablycomposed of the same compound semiconductor material as the firstcladding layer, although the second cladding material may be composed ofany suitable compound semiconductor material many of which arecommercially available or easily producible. In the preferred embodimentthe second cladding layer is composed of AlGaAs. The second claddinglayer may be deposited through any conventional means, such as epitaxialgrowth, chemical vapor deposition, or physical vapor deposition, howeverin the preferred embodiment the second cladding layer is deposited onthe core layer in the same manner that the first cladding layer isdeposited on the undercladding.

The sixth step 20 of the method of is depositing a cap layer on thesecond cladding layer. The cap layer is integral to providing forelectrical contact to the semiconductor laser, as is obvious to thoseskilled in the art. The cap layer is composed of a suitable compoundsemiconductor material compatible with the material of the secondcladding layer. In the preferred embodiment the cap layer is composed ofGaAs. The cap layer can be deposited by any conventional means, such asepitaxial growth, chemical vapor deposition, or high-pressure thermaloxidation.

The seventh step 22 of the method is depositing an upper electricalcontact on the cap layer. The upper contact is typically composed of anOhmic metal and is composed of a material or materials that provide thecorrect electronic work function required to establish a low resistancecontact to the semiconductor material of the cap layer. In the preferredembodiment the upper contact is a p-type Ohmic metal for p-doped GaAssemiconductor material. In a further preferred embodiment the uppercontact is composed of TiPtAu. The upper contact can be deposited by anyconventional means, such as electron beam evaporation, thermalevaporation or sputtering.

As is obvious to those of skill in the art, each of the deposition stepsabove may include additional processing steps, such as polishing,etching, or grinding, to further refine the surfaces of each layer.Every such step is anticipated by this invention and may be used asdesired by those skilled in the art. It is further anticipated that anynecessary surface preparations for addition of a subsequent layer may beperformed, as desired, before a subsequent layer is applied.Additionally, processing may be performed on the cap layer to planarizeor otherwise process the surface before further proceeding with themethod according to user preferences.

The eighth step 24 of the method is etching a trench in the resultantstructure, wherein the trench penetrates the upper contact, cap layer,second cladding layer, core layer, first cladding layer, and auser-definable portion of the undercladding and the trench is of auser-definable width, and wherein the resultant structure is etched suchthat it is substantially L-shaped and includes angling the vertex of thetrench. The resulting shape of the upper contact, cap layer, secondcladding layer, core layer, first cladding layer and undercladding afteretching is substantially L-shaped having two rectangular protrusionstherefrom extending a user-definable length from the vertex of theL-shape. Further, a trench is etched within the stacked structuredescribed. The trench has a substantially U-shaped cross-section and iscreated in an optical semiconductor for a number of purposes. The trenchis necessary for proper performance of the laser, as the trench mustfirst be created prior to creation of some components of the laser.Additionally, in some optical semiconductors the trench can be used tohouse additional components, such as waveguides. As is obvious to thoseof skill in the art, etching of the trench may also result in etching ofthe facets across the core layer, resulting in the creation of mirrorson each side of the resulting trench. The trench can be etched in thestructure by any conventional method, but in the preferred embodiment achlorine based plasma etch is used. In a further preferred embodimentthe structure is etched using BCl₃/Cl₂. In the preferred embodiment,etching is performed to at least the first cladding layer. The goal isto etch through the core layer(s) to a depth that provides maximumtransmission of the optical signal generated by the semiconductor opticdevice. In a further preferred embodiment, the undercladding is etchedto a depth of no greater than 0.5 um past the first cladding layer.Depth into “undercladding” is therefore arbitrary, but a good practicewould probably be to etch no more than 0.5 um past the lowest AlGaAslayer. The width of the trench is user definable, but in the preferredembodiment the narrow section of the trench is approximately 8 um.

The ninth step 26 of the method is depositing a sacrificial spacer layeralong the horizontal and vertical trench surfaces and a user-definableportion of the remaining upper contact. The sacrificial spacer layer ispreferably composed of an oxide material. In a further embodiment thesacrificial spacer layer is composed of SiO₂. The sacrificial spacerlayer is of a user definable thickness, but in a preferred embodiment isapproximately 236.25 nm on the vertical surfaces. The sacrificial spacerlayer can be deposited on the structure by any conventional means, butis preferably deposited using a conformal process.

The tenth step 28 of the method is fabricating a waveguide on thesacrificial spacer layer. In the preferred embodiment, the waveguidematerial fills the remaining portion of the trench, however thewaveguide may fill less than the entire trench according to userpreferences. Any suitable material can be used for the waveguide,however in the preferred embodiment a polymer material is used, such asbenzocyclobutene (BCB.) Any suitable method can be used to deposit thewaveguide on the sacrificial spacer layer, such as spin coating thewaveguide material on the sacrificial spacer layer. Excess waveguidematerial may exist after deposition of the waveguide, such as materialthat has been deposited on the upper contact or that rises above thelevel of the trench. In a preferred embodiment, if any excess materialexists after deposition of the waveguide, it is removed through a plasmaetch process such as reactive ion etching (RIE.) This RIE may beperformed using appropriate plasmas, such as a fluorine based plasma.The removal of the excess guide material exposes the sacrificial spacerlayer material near the regions where gaps are required. This thenallows a wet chemical access to the sacrificial spacer layer material sothat the sacrificial spacer layer can be selectively removed.

The eleventh step 30 of the method is removing the sacrificial spacerlayer from the upper contact and a user-definable portion of the trench.In the eleventh step 30 a user-definable portion of the sacrificialspacer layer is removed to create gaps between the waveguide and theportions of the undercladding, first cladding layer, core layer, secondcladding layer, cap layer, and upper contact that were exposed on eachside of the trench. The sacrificial spacer layer may additionally beremoved from a user-definable portion of the base of the trench, howevera sufficient amount of the sacrificial spacer layer must remain toadhere the waveguide to the base of the trench. The sacrificial spacerlayer can be removed by any conventional means, however in the preferredembodiment it is removed by a timed wet etch. The timed etch ispreferably performed with buffered hydrofluoric acid. The removal of thesacrificial spacer layer material at the vertex of the L-shape of thewaveguide produces a mirror at the vertex. Specifically, as the photonspass through one leg of the L-shaped waveguide they will impact themirror at a given angle of incidence. The photons will then reflect offat an equivalent angle of reflectance down the opposing leg of theL-shaped waveguide through well-known principles of physics.

The result of the above described process is an approximately L-shapedoptical semiconductor device consisting of a laser with an integralwaveguide with side air gaps and a bend mirror in the waveguide. The airgaps exist between the waveguide and the sidewalls of the trench formedby the etching process. This process is less time consuming and morecost efficient than previous methods for creating air gaps in opticalsemiconductor devices as a single step is required for the creation ofthe sacrificial spacer layer and the adhesion layer for the waveguide.Removal of the sacrificial spacer layer also occurs in a single step.Because simple processes are used to achieve each step, the method ofthe present invention creates significant advantages over the prior artinventions.

A product 40 developed by this process is shown in FIG. 2. As can beseen, two straight sections 42 are present in the waveguide, as is oneangled section 44 having a mirror 46 gap therein. The sidewalls,undercladding, first cladding layer, core layer, second cladding layer,and cap layer similarly form an L-shaped section 48 as described. As canfurther be seen trenches 52 exist along the undercladding. Thisstructure includes precisely spaced gaps 54 between components throughthe method described in the present invention to create an integratedwaveguide turning mirror and reduce losses in the waveguide.

The steps of a method of an alternative embodiment are shown in FIG. 3.The first step 60 of the alternative method of FIG. 3 is selecting abase structure. This step is essentially identical to the first step 10of the method if FIG. 1, and therefore will not be discussed in detail.As with the first step 10 of FIG. 1, the base structure in the preferredembodiment is a compound semiconductor.

The second step 62 of the alternative method of FIG. 3 is depositing anundercladding layer on the base structure. As with the second step 12 ofthe method of FIG. 1, this undercladding improves the electricalefficiency of the semiconductor laser structure. The undercladding layercan be deposited by any conventional method, such as epitaxial growth,chemical vapor deposition, or high-pressure thermal oxidation. Theunder-cladding layer is composed of a conventional compoundsemiconductor material. In the preferred embodiment the under-claddinglayer is composed of a III-V semiconductor material, such as GaAs.

The third step 64 of the alternative method of FIG. 3 is depositing afirst cladding layer on the undercladding layer. As is well known tothose in the art, a cladding layer is used in optical semiconductors toincrease optical confinement in the active regions of the opticaldevice. The first cladding layer is a compound semiconductor material,many of which are commercially available or easily producible. In thepreferred embodiment the first cladding layer is composed of AlGaAs. Thefirst cladding layer may be deposited through any conventional means,such as epitaxial growth, chemical vapor deposition, or physical vapordeposition.

The fourth step 66 of the alternative method is depositing at least onecore layer on the first cladding layer. The core layer operates as theactive layer for the semiconductor laser. This core layer is composed ofan appropriate compound semiconductor material that will be determinedbased on the material of the first cladding layer and the requiredoptical properties of the completed optical device. If more than onecore layer is required, a barrier layer with an electrical bandgap thatis larger than the bandgap of the core layers is used to separate thecore layers. In the preferred embodiment two core layers composed ofInGaAs are separated by a barrier layer composed of AlGaAs. The corelayer may be deposited on the first cladding layer by any conventionalmeans, such as epitaxial growth, chemical vapor deposition, or physicalvapor deposition.

The fifth step 68 of the alternative method is depositing a secondcladding layer on the core layer. As was explained with reference to thethird step 64 of the alternative method, a cladding layer increasesoptical confinement in the active regions of the optical device. Thefifth step 68 of the alternative method is essentially identical to thefifth step 18 of the method of FIG. 1, and therefore will not bediscussed in further detail.

The sixth step 70 of the alternative method of FIG. 3 is depositing acap layer on the second cladding layer. The cap layer is integral toproviding for electrical contact to the semiconductor laser, as isobvious to those skilled in the art. The cap layer is composed of asuitable compound semiconductor material compatible with the material ofthe second cladding layer. In the preferred embodiment the cap layer iscomposed of GaAs. The cap layer can be deposited by any conventionalmeans, such as epitaxial growth, chemical vapor deposition, orhigh-pressure thermal oxidation.

The seventh step 72 of the alternative method is depositing an upperelectrical contact on the cap layer. The upper contact is typicallycomposed of an Ohmic metal and is composed of a material or materialsthat provide the correct electronic work function required to establisha low resistance contact to the semiconductor material of the cap layer.In the preferred embodiment the upper contact is a p-type Ohmic metalfor p-doped GaAs semiconductor material. In a further preferredembodiment the upper contact is composed of TiPtAu. The upper contactcan be deposited by any conventional means, such as electron beamevaporation, thermal evaporation or sputtering.

As with the method of FIG. 1, each of the deposition steps above mayinclude additional processing steps, such as polishing, etching, orgrinding, to further refine the surfaces of each layer. Every such stepis anticipated by this invention and may be used as desired by thoseskilled in the art. As was further discussed above in reference to themethod of FIG. 1, it is anticipated in the alternative method that anynecessary surface preparations for addition of a subsequent layer may beperformed, as desired, before a subsequent layer is applied.Additionally, processing may be performed on the cap layer to planarizeor otherwise process the surface before further proceeding with themethod according to user preferences.

The eighth step 74 of the alternative method is etching a trench in theresultant structure, wherein the trench penetrates the upper contact,cap layer, second cladding layer, core layer, first cladding layer, anda user-definable portion of the undercladding and the trench is of auser-definable width. A trench has a substantially U-shapedcross-section and is created in an optical semiconductor for a number ofpurposes. In the alternative embodiment, the etched trench issubstantially L-shaped and includes a section of user-definable widerwidth extending from the vertex of the L-shaped trench a user-definablelength along each leg of the L-shaped trench. The resulting shape is asubstantially L-shaped trench having two rectangular protrusionstherefrom extending a user-definable length from the vertex of theL-shape. The resulting structure will have a uniform width at allsections not associated with a section of the trench having auser-definable wider width. In the remaining sections the trench willhave a width of the user-definable width discussed with reference to thesecond step 62. The trench is not only necessary for proper performanceof the laser, but in some optical semiconductors the trench can be usedto house additional components, such as waveguides. As is obvious tothose of skill in the art, etching of the trench may also result inetching of the facets across the core layer, resulting in the creationof mirrors on each side of the resulting trench. The trench can beetched in the structure by any conventional method, but in the preferredembodiment a chlorine-based plasma etch is used. In a further preferredembodiment the structure is etched using BCl₃/Cl₂. In the preferredembodiment, etching is performed to at least the first cladding layer.The goal is to etch through the core layers to a depth that providesmaximum transmission of the optical signal generated by thesemiconductor optical device. In a further preferred embodiment, theundercladding is etched to a depth of no greater than 0.5 um past thefirst cladding layer. Depth into “undercladding” is therefore arbitrary,but a good practice would probably be to etch no more than 0.5 um pastthe lowest AlGaAs layer. The width of the trench is user definable, butin the preferred embodiment the narrow section of the trench isapproximately 8 um.

The ninth step 76 of the alternative method is depositing a sacrificialspacer layer along the horizontal and vertical trench surfaces and auser-definable portion of the remaining upper contact. The sacrificialspacer layer is preferably composed of an oxide material. In a furtherembodiment the sacrificial spacer layer is composed of SiO₂. Thesacrificial spacer layer is of a user definable thickness, but in apreferred embodiment is approximately 236.25 nm on the verticalsurfaces. The sacrificial spacer layer can be deposited on the structureby any conventional means, but is preferably deposited using a conformalprocess.

The tenth step 78 of the alternative method is fabricating a waveguideon the sacrificial spacer layer. In the preferred embodiment, thewaveguide material fills the remaining portion of the trench, howeverthe waveguide may fill less than the entire trench according to userpreferences. Any suitable material can be used for the waveguide,however in the preferred embodiment a polymer material is used, such asbenzocyclobutene (BCB.) The tenth step 78 is essentially identical tothe tenth step 28 of the method of FIG. 1, and therefore will not bediscussed in further detail.

The eleventh step 80 of the alternative method is depositing a masklayer. In the preferred embodiment a photoresist is used as the masklayer to define the waveguide described in the tenth step 78.

The twelfth step 82 of the alternative method is to pattern the masklayer on the portion of the waveguide deposited within the regionassociated with the trench having a user-definable wider width asdefined in the eight step 74 of the alternative method, wherein the masklayer defines a substantially L-shaped waveguide region having a userdefinable width along each leg of the waveguide at the regions of thetrench that is not of a user-definable wider width. A mask layer definesareas of semiconductor and optical devices, such as the waveguide, toallow a specific or precise design of a device to be achieved. Manytypes of masks and masking processes are known in the art, and any suchmask may be used in conjunction with the present invention.

The thirteenth step 84 of the alternative method is patterning thewaveguide beneath the mask layer. The method of patterning the waveguidewill be dependant on the material used for the mask layer and thematerial used to form the waveguide. In a preferred embodiment, a plasmaetch is used to pattern the waveguide including angling the vertex ofthe L-shape of the waveguide, wherein the angling is performed by meansof etching to produce a mirror. Removal of the corner of the L-shapedwaveguide produces a mirror on the waveguide corner. Specifically as thephotons pass through one leg of the L-shaped waveguide they will impactthe mirror at a given angle of incidence. The photons will then reflectoff at an equivalent angle of reflectance down the opposing leg of theL-shaped waveguide through well-known principles of physics. In apreferred embodiment a reactive ion etch (RIE) process is used topattern the waveguide. In a further preferred embodiment, if any excessmaterial exists after deposition of the waveguide, it is removed througha RIE plasma etch process at the same time as the L-shaped waveguide isdefined. This RIE may be performed using appropriate plasmas, such as afluorine based plasma. The removal of the excess guide material exposesthe sacrificial spacer layer material near the regions where gaps arerequired. This then allows a wet chemical access to the sacrificialspacer layer material so that the sacrificial spacer layer can beselectively removed.

The fourteenth step 86 of the alternative method is removing the masklayer. The removal of the mask layer exposes the underlying waveguide.The resulting waveguide should be substantially L-shaped, as wasexplained in greater detail above. The mask layer is removed by anyprocess appropriate to the material that composes the mask layer. In apreferred embodiment the mask layer is composed of a photoresist,therefore the mask layer is preferably removed by a dry etch, wetchemical etch or other process appropriate to photoresist removal.

The fifteenth step 88 of the alternative method is removing thesacrificial spacer layer from the upper contact and a user-definableportion of the trench. In the fifteenth step 88 a user-definable portionof the sacrificial spacer layer is removed to create gaps between thewaveguide and the portions of the undercladding, first cladding layer,core layer, second cladding layer, cap layer, and upper contact thatwere exposed on each side of the trench. The sacrificial spacer layermay additionally be removed from a user-definable portion of the base ofthe trench, however a sufficient amount of the sacrificial spacer layermust remain to adhere the waveguide to the base of the trench. Thesacrificial spacer layer can be removed by any conventional means,however in the preferred embodiment it is removed by a timed wet etch.The timed etched is preferably performed with buffered hydrofluoricacid.

The result of the process described above is an approximately L-shapedoptical semiconductor device consisting of a laser with an integralwaveguide with side air gaps and an enlarged side trench associated withan etched turning mirror in the waveguide. The air gaps exist betweenthe waveguide and the sidewalls of the trench formed by the etchingprocess. As with the first method, this process is less time consumingand more cost efficient than previous methods for creating air gaps inoptical semiconductor devices as a single step is required for thecreation of the sacrificial spacer layer and the adhesion layer for thewaveguide. Removal of the sacrificial spacer layer also occurs in asingle step. Because simple processes are used to achieve each step themethod of the alternative embodiment creates significant advantages overthe prior art inventions.

A product 90 developed by this process is shown in FIG. 4. As can beseen, two straight sections 92 are present in the waveguide, as is oneangled section 94 having a mirror 96 etched therein. The sidewalls,undercladding, first cladding layer, core layer, second cladding layer,and cap layer similarly form an L-shaped section 98 as described and asection having an increased section of wider width at its vertex 100. Ascan further be seen trenches 102 exist along the undercladding and inthe increased section of wider width. This structure includes preciselyspaced gaps 104 between components through the method described in thealternative embodiment to coherently enhance or reduce reflections fromthe interfaces.

1. An optical semiconductor device, comprising: a) a coherent photonicemitter structure; b) a trench of a user definable width etched in thecoherent photonic emitter structure such that the coherent photonicemitter structure is substantially L-shaped and includes; c) asacrificial spacer layer deposited along a user-definable section of thetrench; d) a waveguide fabricated on the sacrificial spacer layer; ande) a user-definable portion of the sacrificial spacer layer removed. 2.The device of claim 1, wherein the waveguide further comprises: a) awaveguide material deposited on a user-definable portion of thesacrificial spacer layer; and b) excess waveguide material etched awayto form the waveguide.
 3. The device of claim 2, wherein the coherentphotonic emitter structure comprises a coherent photonic emitterstructure, wherein the coherent photonic emitter structure comprises abase structure, a first cladding layer, a core layer, a second claddinglayer, a cap layer and an upper contact.
 4. The device of claim 1,wherein the coherent photonic emitter structure comprises a coherentphotonic emitter structure, wherein the coherent photonic emitterstructure comprises a base structure, a first cladding layer, a corelayer, a second cladding layer, a cap layer and an upper contact.